This study deals with the characterization of functional properties of human T cells, especially suppressor cells, to determine whether they play a role in the pathogenesis of malignant melanoma. The effect of surgical and adjunctive immunotherapy on suppressor cell function will also be examined. Results thus far have included the following: 1) characterization of a 16,000 (p16) molecular weight human T cell antigen which is expressed on human suppressor T lymphocytes, but not the helper T cells, 2) immunochemical purification of a 25,000 (p25) molecular weight antigen on human T cells which is homologous with the Thy-1 T cell antigen in the mouse, 3) characterization of killer (K) cells in ADCC antibody dependent cellular cytotoxicity, demonstrating that such K cells are nonrosetting T cells expressing the p25 antigen, and possibly the p16 antigen, 4) multifactoral analysis (Cox regression model) of 394 Stage I melanoma patients and 185 Stage II melanoma patients identifying the dominant prognostic variables, 5) demonstration that ulceration of a melanoma and a polypoid growth pattern are extremely adverse prognostic findings, 6) demonstration that depressed mitogen responses of melanoma patients are partially restored by incubating the cells with indomethacin, a prostaglandin synthetase inhibitor. Our plans are to prepare monoclonal antisera against the p16 and p25 T cell antigen so that functional subsets of lymphocytes can be better isolated and characterized, and to complete histocompatibility typing studies involving 100 melanoma patients for the HLA-A, B, C, and D loci. This information will be correlated with clinical data and immune function.